This proposal is concerned with the analysis of the ionic mechanisms and metabolic controls involved in the generation of currents and potentials by the vertebrate photoreceptor cell in darkness and in light. The research is directed at understanding the relationships between ionic concentration gradients, transmembrane ionic movements, and ionic active transport processes as well as with the metabolic processes which support these activities. The role of glutathione in the function of this tissue is also under study in relation to the oxidation-reduction state of the retina. Simultaneous measurements of electrical and metabolic activities are made with respect to altered ionic environments, changes in the state of adaptation and different levels of oxygen and glucose availability. Metabolic parameters to be studied include lactate production, oxygen consumption, ATPase activities, and retinal ATP concentrations. Electrical activities, transretinal potentials and the distribution of dark and photocurrents along the photoreceptor cell layer are measured.